docs: def _list_sessions(self):
          """
          Return list of sessions in :py:obj:`dict` form.
  
          Retrieved from ``$ tmux(1) list-sessions`` stdout.
  
          The :py:obj:`list` is derived from ``stdout`` in
          :class:`common.tmux_cmd` which wraps :py:class:`subprocess.Popen`.
  
          Returns
          -------
          list of dict
          """
  
          sformats = formats.SESSION_FORMATS
          tmux_formats = ['#{%s}' % f for f in sformats]
  
          tmux_args = ('-F%s' % '\t'.join(tmux_formats),)  # output
  
          proc = self.cmd('list-sessions', *tmux_args)
  
          if proc.stderr:
              raise exc.LibTmuxException(proc.stderr)
  
          sformats = formats.SESSION_FORMATS
          tmux_formats = ['#{%s}' % format for format in sformats]
          sessions = proc.stdout
  
          # combine format keys with values returned from ``tmux list-sessions``
          sessions = [dict(zip(sformats, session.split('\t'))) for session in sessions]
  
          # clear up empty dict
          sessions = [
              dict((k, v) for k, v in session.items() if v) for session in sessions
          ]
  
          return sessions